linux-kernel - Re: [PATCH -mm] mm, memory-hotpulg: Rename movablenode boot option to movable

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Message-ID: <524A69DA.9050701@cn.fujitsu.com>
Date:	Tue, 01 Oct 2013 14:21:14 +0800
From:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Zhang Yanfei <zhangyanfei.yes@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Wen Congyang <wency@...fujitsu.com>,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	Tang Chen <tangchen@...fujitsu.com>, linux-doc@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>, imtangchen@...il.com
Subject: Re: [PATCH -mm] mm, memory-hotpulg: Rename movablenode boot option
 to movable_node

Hello Ingo,

On 10/01/2013 01:46 PM, Ingo Molnar wrote:
> 
> * Zhang Yanfei <zhangyanfei.yes@...il.com> wrote:
> 
>> @@ -153,11 +153,18 @@ config MOVABLE_NODE
>>  	help
>>  	  Allow a node to have only movable memory.  Pages used by the kernel,
>>  	  such as direct mapping pages cannot be migrated.  So the corresponding
>> +	  memory device cannot be hotplugged.  This option allows the following
>> +	  two things:
>> +	  - When the system is booting, node full of hotpluggable memory can
>> +	  be arranged to have only movable memory so that the whole node can
>> +	  be hotplugged. (need movable_node boot option specified).
> 
> So this is _exactly_ what I complained about earlier: why is the 
> movable_node boot option needed to get that extra functionality? It's 
> clearly not just a drop-in substitute to CONFIG_MOVABLE_NODE but extends 
> its functionality, right?

Generally speaking, CONFIG_MOVABLE_NODE is used to allow a node to have
only movable memory. Firstly, we didn't support the functionality to support
boot-time configuration. That said, before this patchset, we only support
later hot-add node to have only movable memory but any node that is dectected
at boot-time cannot. So here is movable_node option, to protect the kernel
from using hotpluggable memory at boot-time and if a node is full of hotpluggable
memory, this node is arranged to have only movable memory and can be hot-removed
after the system is up.

> 
> Boot options are _very_ poor user interface. If you don't want to enable 
> it by default then turn this sub-functionality into 
> CONFIG_MOVABLE_NODE_AUTO and keep it default-off - but don't pretend that 
> this is only about CONFIG_MOVABLE_NODE alone - it isnt: as described above 
> the 'movable_node' is needed for the full functionality to be available!

As explained above, we need the boot option to only disable boot-time
memory-hotplug configuration not the whole MOVABLE_NODE functionality.

Thanks

-- 
Thanks.
Zhang Yanfei
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